There has conventionally been practiced measurement of circuit parameters (such as the S parameters) of a device under test (DUT). A description will now be given of the measurement method of the circuit parameters of the device under test (DUT) according to the prior art with reference to FIG. 18.
A signal at frequency f1 is transmitted from a signal source 110 to a receiving unit 120 via a DUT 200. The signal is received by the receiving unit 120. It is assumed that the frequency of the signal received by the receiving unit 120 is f2. It is possible to acquire the S parameters and frequency characteristics of the DUT 200 by measuring the signal received by the receiving unit 120.
On this occasion, measuring system errors are generated in the measurement due to mismatching between a measuring system such as the signal source 110 and the DUT 200, and the like These measuring system errors include, for example, Ed: error caused by the direction of a bridge, Er: error caused by frequency tracking, and Es: error caused by source matching. FIG. 19 shows a signal flow graph relating to the signal source 110 if the frequency f1=f2. RF IN denotes a signal input from the signal source 110 to the DUT 200 or the like, Slim denotes an S parameter of the DUT 200 and the like acquired by a signal reflected from the DUT 200 or the like, and S11a denotes a true S parameter of the DUT 200 and the like without measuring system errors.
If the frequency f1=f2, the errors can be corrected in a manner described in a patent document 1 (Japanese Laid-Open Patent Publication (Kokai) No. H11-38054), for example. The correction in this way is referred to as calibration. A brief description will now be given of the calibration. Calibration kits are connected to the signal source 110 to realize three types of state: open, short circuit, and load (standard load Z0). In these states, a signal reflected from the respective calibration kits is acquired by a bridge to obtain three types of the S parameter (S11m) corresponding to the three types of state. The three types of variable Ed, Er, and Es are acquired from the three types of the S parameter.
However, the frequency f1 may not be equal to the frequency f2. For example, the DUT 200 may be a device providing a frequency conversion function such as a mixer. In this case, a measuring system error caused by the receiving unit 120 cannot be neglected. FIG. 20 shows a signal flow graph if the signal source 110 and the receiving unit 120 are directly connected with each other. S21m denotes an S parameter of the DUT 200 and the like acquired based on a signal received by the receiving unit 120. As shown in FIG. 20, there are generated measuring system errors Et (transmission tracking error) and EL caused by the receiving unit 120. These errors cannot be acquired by the calibration as described in the patent document 1.
Therefore, if the frequency f1 is not equal to the frequency 12, the errors are corrected as described in a patent document 2 (WO 03/087856, pamphlet). First, three types of calibration kit (open, short circuit, and load (standard load Z0)) are connected to a signal source This is the same as the method described in the patent document 1, and Ed, Es, and Er can thus be acquired. Further, a signal source 110 and a receiving unit 120 are directly connected with each other, and the transmission tracking errors Et and EL can be acquired based on a measured result on this occasion (refer to FIG. 8 and FIG. 9 in the patent document 2).
It should be noted that the above example is applied to a case where a network analyzer including the signal source 110 and the receiving unit 120 has two ports. If a network analyzer has four ports, two ports are selected from the four ports, and are directly connected with each other, and it is thus necessary to carry out a total of 4×3/2=6 couplings. In general, if a network analyzer has n ports, two ports are selected from the n ports, and are directly connected with each other, and it is thus necessary to carry out a total of n×(n−1)/2 couplings.
However, a large amount of labor is necessary to realize all combinations of two ports by selecting and directly connecting two ports out of the n ports as described above.
An object of the present invention is to reduce the labor required to select and directly connect two ports out of ports of a network analyzer in order to measure transmission tracking errors.